I'd qualify that with 'in the galaxy' and 'at this time'; if you accept the ideal of going from primitive creature to (us) an advanced civilization in less than 25,000 years, it seems reasonable to assume that more could have existed at some point in the past several billion years.
I don’t know if there is other life out there or not
but I think we need to consider.
If
many of us who are alive today spent at least some time
In our young Lives looking at horses rears just going
to town even though they had been making Cars for year’s.and are still making them.
We have not been Exploring space even half that long and
they stopped for years.
The point is that space travel is so new that we have not
even started yet.
But the world could blow up and maybe we will never start.